Wavelength dependency and photosensitizer effects in UV-LED photodegradation of iohexol

Meng-Yuan Xu; Chao Zeng; Yi-Li Lin; Tian-Yang Zhang; Qi Fu; Heng-Xuan Zhao; Zhen-Ning Luo; Zheng-Xiong Zheng; Tong-Cheng Cao; Chen-Yan Hu; Bin Xu

doi:10.1016/j.watres.2024.121477

Wavelength dependency and photosensitizer effects in UV-LED photodegradation of iohexol

Water Res. 2024 May 15:255:121477. doi: 10.1016/j.watres.2024.121477. Epub 2024 Mar 14.

Authors

Meng-Yuan Xu¹, Chao Zeng¹, Yi-Li Lin², Tian-Yang Zhang³, Qi Fu¹, Heng-Xuan Zhao¹, Zhen-Ning Luo¹, Zheng-Xiong Zheng¹, Tong-Cheng Cao⁴, Chen-Yan Hu⁵, Bin Xu⁶

Affiliations

¹ State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Urban Water Supply, Water Saving and Water Environment Governance in the Yangtze River Delta of Ministry of Water Resources, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, PR China.
² Department of Safety, Health and Environmental Engineering, National Kaohsiung University of Science and Technology, Kaohsiung 824, Taiwan, ROC.
³ State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Urban Water Supply, Water Saving and Water Environment Governance in the Yangtze River Delta of Ministry of Water Resources, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, PR China. Electronic address: tianyang1815@126.com.
⁴ School of Chemical Science and Engineering, Key Laboratory of Road and Traffic Engineering of Ministry of Education, Tongji University, Shanghai, 200092, PR China.
⁵ College of Environmental and Chemical Engineering, Shanghai University of Electric Power, Shanghai 200090, PR China.
⁶ State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Urban Water Supply, Water Saving and Water Environment Governance in the Yangtze River Delta of Ministry of Water Resources, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, PR China. Electronic address: tjwenwu@tongji.edu.cn.

PMID: 38520778
DOI: 10.1016/j.watres.2024.121477

Abstract

Iodinated X-ray contrast media (ICM) are ubiquitously present in water sources and challenging to eliminate using conventional processes, posing a significant risk to aquatic ecosystems. Ultraviolet light-emitting diodes (UV-LED) emerge as a promising technology for transforming micropollutants in water, boasting advantages such as diverse wavelengths, elimination of chemical additives, and no induction of microorganisms' resistance to disinfectants. The research reveals that iohexol (IOX) degradation escalates as UV wavelength decreases, attributed to enhanced photon utilization efficiency. Pseudo-first-order rate constants (k_obs) were determined as 3.70, 2.60, 1.31 and 0.65 cm² J^-1 at UV-LED wavelengths of 255, 265, 275 and 285 nm, respectively. The optical properties of dissolved organic matter (DOM) and anions undeniably influence the UV-LED photolysis process through photon competition and the generation of reactive substances. The influence of Cl^- on IOX degradation was insignificant at UV-LED 255, but it promoted IOX degradation at 265, 275 and 285 nm. IOX degradation was accelerated by ClO₂^-, NO₃^-and HA due to the formation of various reactive species. In the presence of NO₃^-, the k_obs of IOX followed the order: 265 > 255 > 275 > 285 nm. Photosensitizers altered the spectral dependence of IOX, and the intermediate photoactivity products were detected using electron spin resonance. The transformation pathways of IOX were determined through density functional theory calculations and experiments. Disinfection by-products (DBPs) yields of IOX during UV-LED irradiation decreased as the wavelength increased: 255 > 265 > 275 > 285 nm. The cytotoxicity index value decreased as the UV-LED wavelength increased from 255 to 285 nm. These findings are crucial for selecting the most efficient wavelength for UV-LED degradation of ICM and will benefit future water purification design.

Keywords: Degradation pathway; Disinfection by-products; Iohexol; UV-LED; Water treatment; Wavelength.